Objective To investigate the expression of programmed death-1(PD-1) and programmed death ligand-1 (PD-L1) in peripheral T-lymphocytes from patients with chronic periodontitis and its significance and to clarify its role in the development of chronic periodontitis.Methods A total of 73 subjects were included in the study and divided into three groups,chronic periodontitis (30 cases),chronic gingivitis(25 cases) and 18 healthy controls.The peripheral blood was collected and PD-1/PD-L1 expression in the surface of CD4+ T lymphocytes and CD8+ T lymphocytes was examined by flow cytometry.Blood samples from 16 chronic periodontitis patients were collected at week 0 and 6 after initial therapy for 6 weeks and PD-1 and PD-L1 expression in the surface of CD4+ and CD8+ T lymphocytes was also determined by flow cytometry.The data were statistically analyzed.Results The percentage of PD-1 expression in CD4+ and CD8+ T lymphocytes of chronic periodontitis group [(16.7 ± 5.5) ％,(20.8 ± 5.1) ％] and chronic gingivitis group [(14.2 ± 6.1) ％,(14.5 ± 4.3) ％] were higher than that of healthy controls [(9.5 ± 2.1) ％,(8.1 ± 1.9) ％] (P ＜ 0.05).The percentage of PD-L1 expression in CD4+ and CD8+ T lymphocytes of chronic periodontitis group [(24.2 ± 7.1) ％,(15.3 ± 6.8) ％] and chronic gingivitis group [(12.4 ±6.0) ％,(11.2 ± 5.5) ％] were higher than that of healthy controls [(4.7 ± 1.2) ％,(3.2 ± 2.3) ％] (P ＜ 0.05).The percentage of PD-1/PD-L1 expression in CD4+ T lymphocytes and CD8+ T lymphocytes of the chronic periodontitis group were significantly decreased after initial therapy(P ＜ 0.05).Conclusions The expression of PD-1 and PD-L1 in peripheral CD4+ T lymphocytes and CD8+ T lymphocyte of chronic periodontitis patients was up-regulated and was associated with periodontal condition.The initial therapy reduced the expression of PD-1 and PD-L1.